Nervous system chapter 3, 4 Flashcards
(73 cards)
1
Q
Central Nervous System
A
Brain
Spinal cord
2
Q
Peripheral Nervous System
type o nerves
A
- Afferent (sensory)
- Efferent (motor)
3
Q
Afferent
A
Sensory
4
Q
Efferent
A
Motor
5
Q
Sensory
A
afferent (arriving)
6
Q
Motor
A
efferent
(exiting)
7
Q
Meninges
made up of 3
A
- dura mater
- arachnoid mater
- pia mater
8
Q
dura mater
A
outer layer
tough and fibrous - layer of protection for the brain
sticks closely to the bones of teh skull, the inside of the vertebral canal it is not so close fitting.
9
Q
Arachnoid mater
A
middle layer
loose mesh of fibres
10
Q
Pia mater
A
inner layer
far more delicate
contains many blood vessels and sticks closely to the surface of the brain and spinal cord
11
Q
what is Cerebrospinal fluid
A
- third protective structure
- space between middle & inner layers of meninges
- circulates through cavities in the brain and through a canal in the centre of the spinal cord
- is clear, watery fluid containing a few cells and some glucose, protein, urea and salts
12
Q
Cerebrospinal fluid 3 functions
A
- protection
- support
- transport
13
Q
cell body
A
- contains the nucleus and responsible for controlling the functioning of the cell
- around nucleus is cytoplasm containing organelles; mitochondria, endoplasmic reticulum, ribsomes and golgi apparatus
14
Q
dendrites
A
- usually fairly short extensions of cytoplasm of cell body
- often highly branched and carry messages, or nerve impulses, into the cell body
15
Q
axon
A
- often a single, long extention of the cytoplasm
- carries nerve impulses away from cell body, usually longer than dendrites
- brain may only be millimetres while from spinal cord to foot may be a metre or so in length
- at end of =axon terminals
16
Q
myelin sheath
A
- layer of fatty material
- most have myelin sheath covering
- nerve fibre- long extention of nerve cell (axon)
- myelinated fibres & unmyelinated fibres
- gaps - nodes of Ranvier
17
Q
3 important functions of myelin sheath
A
- acts as insulator
- protects axon from damage
- speeds up movement of nerve impulses along the axon
18
Q
neurilemma
A
structure around myelin sheath
helps in the repair of injured fibres
19
Q
Synapses
A
gap between axon terminal to dendrite
- axon of one neuron joins with dendrite of another
- neurons dont touch
- small gap between is where messages have to be carried across- neurotransmitters
- neuromuscular junction - axon and skeletal muscle
20
Q
neurotransmitters
A
chemicals that move across synapse
21
Q
neuromuscular junction
A
- tiny gap (synapse)
- axon meets skeletal muscle cell
22
Q
types of neurons are classified by
A
function or structure
23
Q
Functional types of neurons
A
- sensory (afferent)
- motor (efferent)
- interneurons
24
Q
Structural types of neurons (based on the number of extensions from the cell body)
A
- multipolar neurons
- bipolar neurons
- unipolar neurons
- pseudounipolar neurons
25
# functional
Sensory neurons
- afferent
- carry messages from receptors in the sense organs, or in the skin to the central nervous system (brain and spinal cord)
26
# functional
Motor neurons
- efferent
- carry messages from central nervous system to the effectors, the muscles and glands
27
# functional
Interneurons
- located in the central nervous system
- are the link between sensory and motor neurons
- can be called- association neurons, connector neurons, relay neurons
28
# structural
Multipolar
- one axon
- multiple dendrites
- most common type
- includes most interneurons in the brain & spinal cord & motor neurons carrying messages to skeletal muscles
29
# structural
Bipolar
- one axon
- one dendrite
- axon and dendrite can have branches at their ends
- in eye, ear and nose
- take impulses from receptor cells to other neurons
29
# structural
Unipolar
- one extension
- an axon
- not found in humans or other vertebrates
- found in insects
30
# structural
Pseudounipolar
- both unipolar and bipolar
- single axon- separates into 2- axon terminals and dendrites
- most sensory neurons that carry messages to the spinal cord
31
NEURON
a nerve cell
31
NERVE FIBRE
any long extension of cytoplasm of a nerve cell body, although the term usually reffers to an axon
- axons and dendrites of nerve cells are known as nerve fibres
- outside brain and spinal cord, nerve fibres are grouped to form a nerve
- nerve fibres are arranged into bundles by connective tissues, multiple bundles joining together to form a nerve
32
NERVE
bundles of nerve fibres held together by connective tissue
33
depolarised
describes the membrane of a nerve cell when there is no difference in electrical charge between the inside and outside of the membrane
34
depolarisation
process of becoming depolarised
35
leakage channel
a protein channel that is always open
36
membrane potential
the electrical voltage across a membrane of a cell (usually a nerve cell)
| difference across a membrane. specific
## Footnote
resting membrane potential = -70mV
37
potential difference
a difference in electrical charge between two locations
| just a electrical charge difference. broad
38
polarised
describes the situation when the inside of the membrane of anerve cell has a negative electrical charge compared with the outside
39
5 types of receptors
- thermoreceptors
- osmoreceptors
- chemoreceptors
- touch receptors
- pain receptors
40
3 structures that protect the central nervous system
- bone
- membranes called meninges
- cerebrospinal fluid
41
brain is protected by
cranium
42
spinal cord protected by
vertebral canal
43
Meninges
covering the surface of the brain and spinal cord (3 layers of connective tissue forming meninges)
44
nervous system consists of
- brain
- spinal cord
- nerves
45
peripheral nervous system
nerves
46
cerebrospinal fluid as protection
the CSF acts as a shock absorber, cushioning any blows or shocks the CNS may sustain
47
cerebrospinal fluid as support
brain is suspended inside the cranium and floats in the fluid that surrounds it
48
cererbrospinal fluid as transport
the CSF is formed from the blood, the circulates around and through the CNS before eventually re-entering the blood capillaries. During its circulation it takes nutrients to the cells of the brain and spinal cord and carries away their wastes.
49
corpus callosum
a large bundle of nerve fibres that connect the two hemispheres. It cannot be seen on the outside of the brain
50
cerebellum
underneath the rear part of the brain. The folds are less prominent than those of the cerebrum
51
cerebrum
largest part of the brain. The surface is folded into convolutions
52
hypothalamus
cannot be seen on the outside of the brain. It is deep inside the middle of the brain
53
medulla oblongata
joins the brain to the spinal cord
54
sulci
shallow downfolds
55
fissures
deep downfolds
56
folded structures
convolutions (gyri or gyrus)
57
deepest fissure
longitudinal fissue
58
longitudinal fissure
almost separates the two hemispheres in two halves - left and right cerebral hemispheres
59
nervous system
- along with endocrine system coordinates all our voluntary and involuntary actions
- receives and processes information from sense organs and brings about responses
- nerve cells - neurons
- basic structural adn functional units of the whole nervous system, designed for rapid communication of messages in the body
60
structure of neurons
vary in size and shape, all consist of a cell body and 2 different types of extension from the cell - dendrites and the axon
61
what is myelin sheath formed by outside of the brain and spinal cord
schwann cells
62
what is myelin sheath formed by in the brain and spinal cord
oligodendrocytes
63
nerve transmission/action potential (3)
1. depolarisation
2. repolarisation
3. refractory period
64
1 depolarisation
- Sudden increase in membrane potential
- This occurs if the level of stimulation exceeds about 15mV, or the threshold
- When a neuron is stimulated by a neurotransmitter or a sensory receptor, some sodium channels are opened [known as ligand-gated or mechanical-gated channels]
- Once opened, more sodium ions move into the cell, making the intracellular fluid less negative, increasing the potential difference
- If stimulus is strong enough to increase the potential to -55mV, then voltage-gated sodium channels open. This produces the movement of sodium ions into the cells that proceeds independently of the stimulus. Size of the response is not related to the strength of the stimulus. Known as the all-or-none response
- Sodium ions move in the cell and is too great to be balanced by an outward movement of potassium ions, making the inside of the membrane more positive than the outside. Original polarity of the membrane increases, reaching approximately +40mV. This membrane is then said to be depolarised
65
2 repolarisation
- After a short period of time, repolarisation occurs
- Sodium channels close, stopping the influx of sodium ions
- Voltage-gated potassium ions open, increasing the flow of potassium ions out of the cell, making the inside more negative than the outside and decreases the membrane potential. The membrane is repolarised
- Potassium channels remain open longer than what is needed. Resulting in the membrane potential dropping lower than the resting membrane potential, and the membrane is hyperpolarised. Process is called hyperpolarisation.
66
3 refractory period
- Once sodium channels have opened, they quickly become inactivated; meaning they are unresponsive to stimulus
- For a brief period after being stimulated, the membrane will not undergo another action potential. This period is called the refractory period, lasts from when the membrane reaches the threshold of -55mV until it reaches to the resting membrane potential of -70mV
67
chemoreceptors
- Chemoreceptors are stimulated by particular chemicals
- They are present in the nose, making us sensitive to odours, and in the mouth, giving us sensitivity to tastes
- Are also internal chemoreceptors that are sensitive to the composition of body fluids
- Of particular importance are chemoreceptors in certain blood vessels that are sensitive to the pH of the blood and to the concentrations of oxygen and carbon dioxide
- These chemoreceptors are involved in the regulation of the heartbeat and of breathing
67
osmoreceptors
- Osmotic pressure is determined by the concentration of substances dissolved in the water of the blood plasma
- Higher the concentration the greater the osmotic pressure
- Osmoreceptors are located in the hypothalamus and are sensitive to even very small changes in osmotic pressure
- They can stimulate the hypothalamus so that the body’s water content is maintained within vary narrow limits
67
thermoreceptors
- Are able to respond to heat and cold
- Skin thermoreceptors inform the brain (the hypothalamus and the cerebrum) of changes in the temperature outside the body
- Therefore, we are consciously aware of the temperature of our surroundings
- Peripheral thermoreceptors in the skin are nerve endings that are sensitive to either heat or cold, but not both
- Core temperature is monitored by thermoreceptors in the hypothalamus, which detect the temperature of the blood that is flowing through the brain
- Using information received from the skin and from its own thermoreceptors, the hypothalamus can regulate body temperature
67
touch receptors
- (known as mechanoreceptors or pressure receptors), found mainly in the skin
- Number of different types of touch receptors
- Some are close to the surface of the skin and are sensitive to very light touch
- These occur in greater concentrations in areas such as the lips, fingertips, eyelids and external genital organs
- Nerve endings are also associated with the base of each hair follicle
- These respond to any light touch that bends the hair
- Touch receptors close to the skin surface and those attached to the hairs adapt rapidly, and so after a short time we are no longer aware of the touch
- For example, when first putting on clothing we are aware of it touching the skin, but that sensation disappears very quickly
- Other touch receptors are located deeper in the skin and are sensitive to pressure and vibrations
67
pain receptors
- Also called nociceptors are stimulated by damage to the tissues, such as from a cut or a heavy bump, by poor blood to a tissue, or by excessive stimulation from stimuli such as heat or chemicals
- The receptors for pain are especially concentrated in the skin and the mucous membranes, they occur in most organs, but not in the brain
- Pain is uncomfortable, but it is essential for our wellbeing
- Pain warns us that damage to tissues is occurring, and we can therefore take evasive action or seek medical help so that damage is minimised
- Unlike many other receptors, pain receptors adapt little or not at all, so that pain continues for as long as the stimulus is present
- In some cases, prolonged stimulation of pain receptors makes the pain worse. The failure of pain receptors to adapt keeps the person aware that a tissue-damaging situation exists
